Whether an MU-2, a lowly Seneca I or a high powered jet, it takes rudder to stop the yaw when one engine is making lots more thrust than the other. The MU-2 has a reputation of being less forgiving than many when slow on one engine. This is well known throughout the bizav community. Any pilot transitioning into this type knows (or should know) they need to remain ready for that eventuality. But humans being human...
The two questions that come immediately to mind are:
1) Why did the engine fail?
2) Why didn't the pilot apply sufficient corrective input to maintain control?
There are a multitude of possible answers to each of the above questions and when there is more information available from which to draw inferences, I'll be more willing than I am now to speculate. If no "smoking gun" is found to exist, this one might not be that easy to pin down. We'll see I guess...
westhawk